Laser robots have found various applications, and their use as welding robots has attracted much attention recently. In butt welding and the like, however, there are found a large number of non uniform gaps between workpieces, and a laser beam has a considerably small spot diameter. There arises a problem that sufficient welding results cannot be achieved without performing weaving weld in which the illuminating direction of the laser beam is changed. For the use of the laser robots as the welding robots, it is necessary to improve the weaving performances thereof.
It has been known that a system for imparting weaving function to the laser robots can be roughly divided into two types.
One of the types is a system conventionally used for arc welding robots and the like, in which a laser torch LT is moved in the direction of a beveled edge while the laser torch LT itself is periodically fluctuated in the direction perpendicular to the direction of the beveled edge, as shown in FIG. 43(a) (arrow A1).
The other is a system in which the laser torch LT is moved in the direction of the arrow A2 of FIG. 43(b) along the beveled edge while the deflection angle of the laser beam emitted from the laser torch LT is periodically changed as indicated by the arrow A3. For achievement of the system of the second type, there are two known methods:
(1) a method of periodically vibrating or fluctuating a condenser lens for the laser beam, and
(2) a method of deflecting the laser beam by the combination of a pair of galvano mirrors.
The first system however, has a problem that welding speed is low because an arm for fluctuating the torch cannot be moved at a very high speed.
In the method (1) of the second system, it is necessary to equip the leading edge portion of the arm with a lens drive mechanism since the condenser lens is mounted adjacent to the leading edge of the arm. This structure increases the size and inertia of the leading edge portion of the arm, resulting in increased interference between the leading edge portion of the arm and obstructions and deterioration in controllability.
In the method (2) of the second system, there arises a problem that drive control for the galvano mirrors is not easy. That is, since a laser used for welding is a high power laser (e.g., a carbon dioxide laser of CW oscillation type), the material and thickness of the galvano mirrors are required to resist the high power, and the inertia of the galvano mirrors necessarily increases. Since the galvano mirrors must be vibrated at high frequencies, a torque load on a vibrating mechanism for the galvano mirrors changes violently. As a result, the vibrations of the respective galvano mirrors are difficult to be in synchronism with each other.
These problems are not limited to the welding robots but are common to the laser robots in which the laser beam is required to be deflected periodically.